It turns out Spotify uses P2P technology so that it can reduce the load on it’s servers. Great, except that uses a fair amount of bandwidth and sometimes that’s not OK.
The client always falls back on their central servers, so we could just block P2P. Problem is that we’re given no manual option to disable, (or limit) P2P sharing. Worse still, the client spawns connections to other users within a massive range of ports making them tricky to block.
I just spent the last few hours looking at this because my bandwidth quota has been destroyed, I’ve got a few ideas and some of them have worked.